When using Ext.define() to define an override, I get the expected result in at least one browser but a fatal error in others. Errors are read from either Firebug or the Chrome Developer console.

Interestingly, the override works in Firefox 3.6 on Ubuntu Linux.

Tested with Firefox 3.6.24 on Ubuntu Linux: Application displays properly with anticipated result
Tested with Firefox 9.0.1 on Windows: c is not a constructor
Tested with Chrome 16.0.912.63 on Ubuntu Linux: Uncaught TypeError: object is not a function
Tested with Chrome 16.0.912.75m on Windows: Uncaught TypeError: object is not a function